Per- and polyfluoroalkyl substances (PFASs) are a group of manmade fluorinated organic compounds widely used in industrial and consumer products such as stain repellents, food packaging materials, waxes, adhesives, and aqueous film forming foams (AFFFs) used to extinguish fuel fires. Due to the widespread use of PFASs, these substances have been detected worldwide in the environment, wildlife, and humans (Ahrens and Bundschuh, 2014; Jian et al., 2017; Paul et al., 2009).

The major PFAS exposure routes for humans are ingestion of contaminated food and drinking water and inhalation of dust and air (Gao et al., 2015; Haug et al., 2011; Nilsson et al., 2013; Trudel et al., 2008; Worley et al., 2017; Zhou et al., 2014). The most studied PFASs are the perfluoroalkyl acids (PFAAs) perfluorooctanoic acid (PFOA), perfluorohexane sulfonate (PFHxS) and perfluorooctane sulfonate (PFOS), which are persistent and bioaccumulative (Jian et al., 2018). Previous biomonitoring of individuals after the end of elevated PFAS exposure showed estimated half-lives of 1.8–3.9 years for PFOA, 2.9–15.5 years for PFHxS, and 2.9–5.4 years for PFOS (Brede et al., 2010; Li et al., 2018; Olsen et al., 2007; Worley et al., 2017; Xu et al., 2020). Recently, the half-life of lesser studied perfluoroheptane sulfonate (PFHpS) was reported to be 1.5–2.9 years (Li et al., 2019; Xu et al., 2020). The estimated half-lives show variations between study populations, as well as inter-individual variation within study populations, which have not yet been adequately explored. This variation suggests that some individuals may be at greater risk of accumulating high concentrations of PFASs. Epidemiological studies have suggested that PFAA exposure may be associated with several adverse health effects, and populations impacted by elevated PFAS exposure may experience elevated psychosocial stress (Bach et al., 2015; Ballesteros et al., 2017; Calloway et al., 2020; Kirk et al., 2018; Lazarevic et al., 2021; Steenland et al., 2010; Zhao et al., 2020).

Firefighters may be occupationally exposed to PFASs through inhalation of PFASs present in smoke, air and dust during firefighting, and at firefighting stations. However, the main PFAS exposure is thought to be through inhalation of aerosolized foam, contamination of personal protective equipment (PPE), as well as direct or indirect skin contact and hand to mouth transfer during the use of fluoro-surfactant based firefighting foams, such as AFFFs (Peaslee et al., 2020; Seow, 2013; Shaw et al., 2013; Tao et al., 2008). Elevated serum PFAS concentrations, in comparison to a reference population, have been reported in firefighters from different parts of the world (Dobraca et al., 2015; Graber et al., 2021; Khalil et al., 2020; Leary et al., 2020; Rotander et al., 2015; Seow, 2013; Shaw et al., 2013). However, these studies are predominately cross-sectional analyses of PFAS exposure in firefighters. Although Laitinen et al. (2014) assessed PFAS serum concentrations in eight firefighters over a three month period, the short temporal period and the limited number of participants limits any conclusions. Thus, temporal exposure trends of firefighters to PFAS are largely unknown.

AFFF containing PFASs have been used globally since the 1960s to extinguish hydrocarbon-fuel and chemical solvent fires during aviation incidents, such as aircraft crashes and storage tank fires, and during training exercises (Rotander et al., 2015; Taniyasu et al., 2015). Due to concerns over PFASs exposure and the subsequent introduction of restrictions to reduce exposure, a movement to replace AFFF with non-fluorinated firefighting foams was initiated. In Australia, where AFFF has been used since the 1970s, several agencies have replaced fluoro-surfactant based firefighting foams in the past two decades (Personal Communication with Airservices, 2018; NSW, 2021). To determine whether the replacement of firefighting foams successfully reduces PFAS exposure, it is necessary to monitor PFAS serum concentrations in firefighters over time.

In 2013–2014, Rotander et al. (2015) assessed serum PFAS levels in 149 employees of an Australian organisation offering aviation rescue and firefighting services at airports. The organisation used AFFF for firefighting training and emergencies until approximately 2010, when AFFF foams were replaced by fluoro-surfactant free firefighting foam. At the time of serum collection in 2013–2014, mean serum PFOS and PFHxS concentrations among participating firefighters were six to ten times higher than the mean concentrations of the general Australian population (Rotander et al., 2015). PFAS serum concentrations ranged from 3.4 to 391 ng/mL for PFOS, 0.7–277 ng/mL for PFHxS and 0.3–18 ng/mL for PFOA (Rotander et al., 2015).

In the present study, current and former firefighting staff from the same organisation previously investigated by Rotander et al. (2015) in 2013–2014 (referred to as the “2013–2014 Study”) were approached to participate in a second exposure study. Participants in the earlier study were specifically targeted for recruitment. The overall aim of the study was to determine if the implemented work health and safety measures, such as replacement of AFFF, had been effective in reducing PFAS exposure given that staff continued to work at PFAS contaminated sites. The objectives were to: 1) assess the PFAS serum concentration in current and former firefighting staff; 2) compare the concentrations of PFASs in the participants in this study to the 2013–2014 study, and estimate individual apparent half-lives; and, 3) assess associations between PFAS concentrations and half-lives with potential explanatory factors explored in the questionnaire.